Predrill prediction of subsalt pore pressure from seismic impedance

Abstract

A target-oriented, predrill, pore-pressure prediction method using seismically estimated acoustic impedance is applied to recently acquired and processed dual-coil data in the Green Canyon and Walker Ridge areas of the Gulf of Mexico. Three deepwater subsalt wells are used in the study. One was used as a calibration well, and the other two were used as blind wells for comparing prediction results with the measured pore-pressure and mud-weight data. All three wells are in the Green Canyon area, penetrating thick salt bodies. A new seismic-inversion method is used for inversion of seismic impedance. The pore-pressure method uses a direct transform of the inverse of acoustic impedance, with two adjustable parameters. The optimization of the parameters is done through an iterative process to match the pore-pressure gradient obtained from the well acoustic impedance with those of pore-pressure measurements and mud weights within a tolerable range of those data for the calibration well. The optimized parameters are then used to transform the seismic acoustic-impedance volume to pore-pressure gradient volume. The predicted pore pressure at the blind wells from the well impedance and seismic impedance match reasonably with well data.